Field of the Invention
The present invention relates to an imaging device.
Description of Related Art
An endoscope system capable of performing special light observation using infrared light in addition to normal observation using visible light is widely used. In the endoscope system, it is possible to treat a lesion found through normal observation or the special light observation with a treatment tool.
For example, in an endoscope system disclosed in Japanese Unexamined Patent Application, First Publication No. H10-201707, a fluorescent substance called indocyanine green (ICG) is irradiated with excitation light, and fluorescence from a lesion is detected. The ICG is administered to a body of a test target in advance. The ICG is excited in an infrared region by the excitation light and emits fluorescence. The administered ICG is accumulated into a lesion such as cancer. Since strong fluorescence is generated from the lesion, it is possible to determine the presence or absence of a lesion according to a captured fluorescence image.
In the endoscope system disclosed in Japanese Unexamined Patent Application, First Publication No. H10-201707, a subject is irradiated with light including visible light and infrared light. The infrared light includes excitation light. Light reflected by the subject and fluorescence (infrared fluorescence) generated from the subject are imaged via a dichroic mirror or a dichroic prism built into a camera head. Since a splitting means that performs splitting into the visible light and the fluorescence is provided, it is possible to simultaneously perform normal observation using the visible light and special light observation using the infrared light. Further, the fluorescence, the red light, the green light, and the blue light are imaged by respective different image sensors via the dichroic mirror or the dichroic prism. Therefore, it is possible to obtain a high-quality image.
FIG. 19 shows a configuration of an endoscope device 1001 that is the same as the configuration disclosed in Japanese Unexamined Patent Application, First Publication No. H10-201707. As shown in FIG. 19, the endoscope device 1001 includes a light source unit 1010, an endoscope scope unit 1020, a camera head 1030, a processor 1040, and a monitor 1050. In FIG. 19, a schematic configuration of the light source unit 1010, the endoscope scope unit 1020, and the camera head 1030 is shown.
The light source unit 1010 includes a light source 1100, a band pass filter 1101, and a condenser lens 1102. The light source 1100 emits light having wavelengths from a wavelength band of visible light to a wavelength band of infrared light. The wavelength band of the infrared light includes a wavelength band of excitation light and a wavelength band of fluorescence. The wavelength band of the fluorescence is a band in which a wavelength is longer than that in the wavelength band of the excitation light in the wavelength band of the infrared light. The band pass filter 1101 is provided on an illumination light path of the light source 1100. The band pass filter 1101 transmits only the visible light and the excitation light. The condenser lens 1102 condenses the light transmitted through the band pass filter 1101. A wavelength band of the infrared light emitted from the light source 1100 has only to include at least a wavelength band of the excitation light.
FIG. 20 shows transmission characteristics of the band pass filter 1101. A horizontal axis of a graph shown in FIG. 20 indicates wavelength, and the vertical axis indicates transmittance. The band pass filter 1101 transmits light in a wavelength band in which a wavelength is about 370 nm to about 800 nm. Further, the band pass filter 1101 filters out light in a wavelength band in which a wavelength is shorter than about 370 nm and light in a wavelength band in which a wavelength is equal to or longer than 800 nm. The wavelength band of light transmitted by the band pass filter 1101 includes a wavelength band of the visible light and a wavelength band of the excitation light. The wavelength band of the excitation light is a band in which the wavelength is about 750 nm to about 780 nm. The wavelength band of the light filtered out by the band pass filter 1101 includes a wavelength band of the fluorescence. The wavelength band of the fluorescence is a band in which the wavelength is equal to or longer than about 800 nm.
The endoscope scope unit 1020 includes a light guide 1200, an illumination lens 1201, an objective lens 1202, and an image guide 1203. The light from the light source 1100 is incident on the light guide 1200 via the band pass filter 1101 and the condenser lens 1102. The light guide 1200 transfers the light from the light source 1100 to a distal end portion of the endoscope scope unit 1020. A subject 1060 is irradiated with the light transferred by the light guide 1200, by the illumination lens 1201.
At the distal end portion of the endoscope scope unit 1020, the objective lens 1202 is provided adjacent to the illumination lens 1201. Light reflected by the subject 1060 and fluorescence generated from the subject 1060 are incident on the objective lens 1202. The light reflected by the subject 1060 includes visible light and excitation light. That is, light including the visible light, the excitation light, and the fluorescence is incident on the objective lens 1202. The objective lens 1202 images the light.
A distal end surface of the image guide 1203 is arranged at an image formation position of the objective lens 1202. The image guide 1203 transfers an optical image formed on the distal end surface to a proximal end surface.
The camera head 1030 includes an image formation lens 1300, a dichroic mirror 1301, an excitation light cut filter 1302, an image sensor 1303, a dichroic prism 1304, an image sensor 1305, an image sensor 1306, and an image sensor 1307. The image formation lens 1300 is arranged to face the proximal end surface of the image guide 1203. The image formation lens 1300 forms an optical image transferred by the image guide 1203 on the image sensor 1303, the image sensor 1305, the image sensor 1306, and the image sensor 1307.
The dichroic mirror 1301 is arranged on an optical path from the image formation lens 1300 to an image formation position of the image formation lens 1300. The light passing through the image formation lens 1300 is incident on the dichroic mirror 1301. The dichroic mirror 1301 transmits the visible light and reflects light other than visible light. FIG. 21 shows characteristics of reflection and transmission of the dichroic mirror 1301. A horizontal axis of a graph shown in FIG. 21 indicates wavelength, and a vertical axis indicates transmittance. The dichroic mirror 1301 transmits light in a wavelength band in which a wavelength is shorter than about 700 nm. Further, the dichroic mirror 1301 reflects light in a wavelength band in which a wavelength is equal to or longer than 700 nm. The wavelength band of the light transmitted by the dichroic mirror 1301 includes a wavelength band of the visible light. The wavelength band of the light reflected by the dichroic mirror 1301 includes a wavelength band of infrared light.
An optical image of a visible light component is formed at the image formation position of the light transmitted through the dichroic mirror 1301. On the other hand, an optical image of an infrared light component is formed at the image formation position of the light reflected by the dichroic mirror 1301.
The light reflected by the dichroic mirror 1301 is incident on the excitation light cut filter 1302. The light incident on the excitation light cut filter 1302 includes the infrared light. The infrared light includes excitation light and fluorescence. The excitation light cut filter 1302 filters out the excitation light, and transmits the fluorescence. FIG. 22 shows transmission characteristics of the excitation light cut filter 1302. A horizontal axis of a graph shown in FIG. 22 indicates wavelength, and a vertical axis indicates transmittance. The excitation light cut filter 1302 filters out the light in a wavelength band in which a wavelength is shorter than about 800 nm. Further, the excitation light cut filter 1302 transmits light in a wavelength band in which a wavelength is equal to or longer than about 800 nm. The wavelength band of the light filtered out by the excitation light cut filter 1302 includes the wavelength band of the excitation light. The wavelength band of the light transmitted by the excitation light cut filter 1302 includes the wavelength band of the fluorescence.
The fluorescence transmitted through the excitation light cut filter 1302 is incident on the image sensor 1303. The image sensor 1303 generates an IR signal according to the fluorescence.
FIG. 23 shows characteristics of ICG that is administered to the subject 1060. horizontal axis of a graph shown in FIG. 23 indicates wavelength, and a vertical axis indicates intensity. In FIG. 23, characteristics of the excitation light that excites ICG and characteristics of the fluorescence emitted from ICG are shown. A peak wavelength of the excitation light is about 770 nm, and a peak wavelength of the fluorescence is about 820 nm. Thus, when the subject 1060 is irradiated with the excitation light having a wavelength of about 750 nm to about 780 nm, the fluorescence having a wavelength of about 800 nm to about 850 nm is generated from the subject 1060. By detecting the fluorescence emitted from the subject 1060, it is possible to detect the presence or absence of cancer. As shown in FIG. 20, the band pass filter 1101 transmits the excitation light having a wavelength of about 750 nm to about 780 nm, and filters out the fluorescence having a wavelength of about 800 nm to about 850 nm. Further, as shown in FIG. 22, the excitation light cut filter 1302 filters out the excitation light having a wavelength of about 750 nm to about 780 nm. Therefore, the image sensor 1303 can detect only the fluorescence.
The light in the visible light band transmitted through the dichroic mirror 1301 is incident on the dichroic prism 1304. The dichroic prism 1304 splits the light in the visible light band into light (red light) in a red wavelength band, light (green light) in a green wavelength band, and light (blue light) in a blue wavelength band. The red light passing through the dichroic prism 1304 is incident on the image sensor 1305. The image sensor 1305 generates an R signal according to the red light. The green light passing through the dichroic prism 1304 is incident on the image sensor 1306. The image sensor 1306 generates a G signal according to the green light. The blue light passing through the dichroic prism 1304 is incident on the image sensor 1307. The image sensor 1307 generates a B signal according to the blue light.
The processor 1040 generates a visible light image signal from the R signal, the G signal, and the B signal, and generates a fluorescence image signal from the IR signal. The monitor 1050 displays a visible light image according to the visible light image signal, and a fluorescent image according to the fluorescence image signal. For example, the monitor 1050 displays the visible light image and the fluorescence image acquired at the same time, side by side. Alternatively, the monitor 1050 superimposes and displays the visible light image and the fluorescence image acquired at the same time.